A CMP apparatus is a semiconductor apparatus for polishing a wafer chemically and mechanically. In general, the CMP apparatus includes a carrier for holding the wafer and a surface plate with a polishing pad attached on a top surface thereof. The wafer is pressed against a top of the polishing pad by the carrier. In this state, the surface plate and the carrier can be rotated relative to each other. A new slurry is continuously supplied from a slurry feeder to the top of the polishing pad, so that the precision of polishing and polishing rate of the wafer can be improved.
Two types of slurry are conventionally used for the polishing of the wafer. One is of a slurry containing ammonia-fumigated silica for polishing an interlayer insulating film of the wafer and the other is of a slurry containing alumina for polishing a metal film. The former is of an alkali slurry of about pH 11 containing a predetermined concentration of silica uniformly distributed in deionized water while the latter is of an acid slurry of about pH 2 to 4 containing an oxide agent for oxidizing a metal dissolved in the deionized water. Accordingly, the selection of the slurry type is made depending on whether the interlayer insulation film of the wafer is to be polished or the metal films are to be polished. Whichever the case may be, both the concentration of the abrasives such as silica and so on and the pH of the slurry should be maintained at a predetermined level and a predetermined range, respectively, in order to obtain a desired polishing rate.
However, the conventional CMP process has a certain drawback in that the deionized water used to dilute the concentration of the slurry or to clean the wafer in the CMP process causes several undesirable side effects. For example, since the deionized water causes the concentration and the pH of the slurry after the CMP process to be changed to those different from the predetermined desired level and range, the polishing rate and flatness of the wafer are greatly reduced and, therefore, the slurry once used cannot be reused.
Since the slurry once used is accommodated in a waste bath and thrown away, a great amount of slurry is wasted during the CMP process and, therefore, polishing costs increase. Further, a considerable amount of pH agent discharged out without being recovered causes environmental pollution.